This invention relates to light sources used in optoelectric modules and the like.
More particularly, the present invention relates to light source monitoring apparatus used in optoelectric modules and other electronic equipment.
In optical-to-electrical and electrical-to-optical (hereinafter xe2x80x9coptoelectricxe2x80x9d) modules used in the various communications fields, one of the most difficult problems that must be solved i s the efficient transmission of light between a light generating device and an optical fiber or, alternatively, the transmission of light from the optical fiber to a light receiving device. Here it will be understood by those skilled in the art that the term xe2x80x9clightxe2x80x9d is a generic term which includes any electromagnetic radiation that can be modulated and transmitted by optical fibers or other optical transmission lines.
Because of light losses due to misalignment of optical components and other losses in the system, it is often necessary to drive light sources, such as lasers, light emitting diodes, etc. harder (i.e., provide more current) to provide sufficient light for proper operation. Also, because of minor changes in alignment of components, differences in components (although they may still be within a specified tolerance), aging of components and especially the light source itself, and other factors, it is often necessary to change the amount of drive to the light sources between similar optoelectric apparatus and in a specific appatratus over a lifetime. For example, it is well know in the art that the light output of semiconductor laser (including vertical cavity surface emitting lasers xe2x80x98VCSELsxe2x80x99, edge emitting lasers, etc.) varies with changes in conditions.
It is understood by those skilled in the art that too much drive to a light source results in wasted power, overheating, reduced life cycle, and other problems. However, too little drive to a light source results, in improper operation, possible loss of information in data systems, random errors, and many other problems. Thus, it is highly desirable to provide drive to light sources that is as close to optimum as possible. To achieve this result it is generally desirable to continuously monitor the output of the light source to ensure a constant level of light output. A variety of light source monitors have been proposed in the prior art. However, these prior art monitoring systems are generally complicated and expensive to incorporate into optoelectric modules and other apparatus.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object the present invention to provide new and improved light source monitoring apparatus.
Another object of the present invention is to provide new and improved light source monitoring apparatus which uses a minimum number of components in the system.
And another object of the present invention is to provide new and improved light source monitoring apparatus which improves the efficiency of optical systems.
Still another object of the present invention is to provide new and improved light source monitoring apparatus which allows the use of a variety of components and component materials.
Briefly, to achieve the desired objects of the present invention in accordance with a preferred embodiment thereof, provided is light source monitoring apparatus including a light source designed to produce a beam of light. The light source includes drive electronics connected to the light source to supply a desired amount of drive current to the light source. A monitor diode is connected to the drive electronics to control the amount of drive current supplied to the light source by the drive electronics. A lens system is positioned to receive the beam of light from the light source and transmit substantially all of the beam of light to a light terminal. The lens system includes an optical element and a light reflecting surface on the optical element positioned to reflect a portion of the beam of light onto the monitor diode.
In a preferred embodiment the lens system includes a pair of lens elements defining an optical axis and directing light from the light source into an optical fiber. A first of the lens elements is positioned along the optical axis adjacent the light source and a second of the lens elements is positioned along the optical axis adjacent the light terminal. The light reflecting surface can be, for example, the back of the second lens element or it can be a third optical element and positioned along the optical axis and between the first and second lens elements to reflect a portion of the beam of light at an angle to the optical axis onto the monitor diode. Further, the first and second lens elements (and the adjacent light source and light terminal, respectively) can be housed in separate structural portions that are later assembled to form a complete unit.